The present invention generally relates to the field of intravascular medical devices, and more specifically to the field of catheters such as guide catheters used for the placement of medical devices and diagnostic catheters used to inject radiopaque fluids within the body for treatment and diagnosis of vascular diseases. In particular, the present invention relates to an improved reinforced guide or diagnostic catheter and methods of manufacture.
Several types of catheters are utilized for intravascular treatment. Examples of intravascular catheters include guide catheters, angioplasty catheters, stent delivery devices, angiography catheters, neuro catheters, and the like.
Guide catheters are commonly used during coronary angioplasty procedures to aid in delivering a balloon catheter or other interventional medical devices to a treatment site in a coronary vessel. In a coronary angioplasty procedure, a guide catheter is introduced into a peripheral artery and advanced over a guidewire through the aorta until the distal end of the guide catheter is engaged with the appropriate coronary ostium. Next, a balloon dilatation catheter is introduced over a guidewire and through the guide catheter. The guidewire is advanced past the distal end of the guide catheter within the lumen of the diseased vessel and manipulated across the region of the stenosis. The balloon dilatation catheter is then advanced past the distal end of the guide catheter, over the guidewire, until the balloon is positioned across the stenotic lesion. After the balloon is inflated to dilate the blood vessel in the region of the stenotic lesion, the guidewire, balloon dilatation catheter and guide catheter are withdrawn.
Guide catheters typically have preformed bends formed along their distal portion to facilitate placement of the distal end of the guide catheter into the ostium of a particular coronary artery of a patient. In order to function efficiently, guide catheters generally require a relatively stiff main body portion and soft distal tip. The stiff main body portion gives the guide catheter sufficient xe2x80x9cpushabilityxe2x80x9d and xe2x80x9ctorqueabilityxe2x80x9d to allow the guide catheter to be inserted, moved and rotated in the vasculature to position the distal end of the catheter at the desired site adjacent to a particular coronary artery. However, the distal portion should have sufficient flexibility so that it can track over a guidewire and be maneuvered through a tortuous path to the treatment site. In addition, a soft distal tip at the very distal end of the catheter should be used to minimize the risk of causing trauma to a blood vessel while the guide catheter is being moved through the vasculature to the proper position.
Angiography catheters can be used in evaluating the progress of coronary artery disease in patients. Angiography procedures are used to view the patency of selected blood vessels. In carrying out this procedure, a diagnostic catheter having a desired distal end curvature configuration may be advanced over a guidewire through the vascular system of the patient until the distal end of the catheter is steered into the particular coronary artery to be examined.
For most intravascular catheters, it is desirable to have both a small outer diameter and a large inner lumen. Having a small outer diameter allows the catheter to be maneuvered more easily once inserted into the body, and may allow the catheter to reach more distal sites. Having a large inner lumen allows larger medical appliances to be inserted through the catheter and/or allows a higher volume of fluids to be injected through the inner lumen. To minimize the outer diameter of the catheter and maximize the inner diameter of the inner lumen, a relatively thin catheter wall is needed.
Thin-walled catheters formed strictly from polymers such as polyether block amide often do not have sufficient strength to be useful in many medical procedures. The pushability, torqueability, kinkability and other characteristics are often not acceptable. One way to increase the strength of such a thin-walled catheter is to provide a reinforcing braid or coil in the catheter wall. One such catheter is shown in U.S. Pat. No. 4,516,972 to Samson. Samson discloses an intravascular catheter that has an inner lubricious layer (e.g., PTFE), an intermediate reinforcing layer (braid), and an outer layer. The inner lubricious layer reduces the friction of the wall of the inner lumen, which is particularly useful when dilatation catheters or other medical devices are passed through the inner lumen. The braided reinforcing layer is braided over the lubricious layer, and the outer layer is extruded over the reinforcing layer.
While Samson improves the strength of the catheter wall, the ability to minimize the thickness of the catheter wall is limited. For example, the minimum thickness of the inner lubricous layer of Samson typically must be sufficiently thick to ensure that the lubricious layer remains structurally intact during subsequent processing steps, such as when the reinforcing layer is braided thereover. In addition, the braided reinforcing layer does not penetrate the outer surface of the inner lubricious layer. Instead, the braided reinforcing layer overlays the outer surface of the lubricious layer. As such, the braided reinforcing layer does not share the same space as the inner lubricious layer, thereby adding to the overall thickness of the catheter wall. Finally, because three separate layers must be assembled to form the catheter, the manufacturing costs may be relatively high.
The present invention provides a reinforced catheter shaft that may have a reduced wall thickness and/or lower manufacturing cost than the prior art. This is preferably achieved by eliminating or reducing the thickness of the inner lubricious layer and/or allowing the reinforcing layer to share the same space as the inner lubricious layer. In one illustrative embodiment, the inner lubricious layer is removed altogether, and an inner tubular formed braid member defines the inner lumen of the catheter shaft. In another illustrative embodiment, the inner lubricious layer and the reinforcing layer are effectively combined to form a reinforcing member. This is accomplished by, for example, coating the wires used to form the reinforcing member with a lubricious polymer such as polytetrafluoroethylene (PTFE) or perfluoroalkoxy (PFA) to first form coated wire. When these coated wires are wound or braided on a mandrel to form the tubular reinforcing member, the inner surface of the reinforcing member includes the lubricious polymer exposed to the inner lumen and forming the lumen wall.
To provide a smooth inner surface on the lumen wall, the braided or wound reinforcing member may first be disposed on a mandrel that has a relatively smooth outer surface. Heat and/or pressure may then be used to cause the lubricious polymer that coats the core wires of the reinforcing member to conform to the outer surface of the mandrel.
If a non-thermoplastic polymer such as PTFE is used to coat the core wires, significant heat and pressure may be required to induce the non-thermoplastic polymer to conform to the outer surface of the mandrel. In such a case, the mandrel may be metallic, and more specifically, may be copper or copper coated with silver. If a thermoplastic polymer such as a perfluoroalkoxy polymer (PFA or MFA) is used to coat the core wires of the reinforcing member, less heat may be required to induce the thermoplastic polymer to flow and conform to the smooth outer surface of the mandrel. Accordingly, the mandrel may be made from a polymer, such as acetyl polymer. In this latter case, the cost of the mandrel may be significantly reduced relative to a copper or silver coated copper mandrel. In either case, an outer layer is preferably extruded over the reinforcing member to provide additional support to the catheter shaft and to provide a smooth outer surface.